Magnetic shield for electrical apparatus



Jan. 25, 1944. L. E. SAUER MAGNETIC SHIELD FOR ELECTRICAL APPARATUSFiled April 11, 1941 INVENTOR 1 010's .5. Sal/err BY M :7

WITNESSES:

ATTORN EY Patented Jan. 25, 1944 I UNITED STATES "PATENT OFFICE MAGNETICSHIELD FOR ELECTRICAL APPARATU Louis E. Sauer, Sharon, Pa.,

assignor to Westinghouse Electric & Manufacturing Company,

East Pittsburgh, Pa.,

nia

a corporation of Pennsyl- Application April 11, 1941, SerialNo. 388,070Claims. (01. 175-361) My invention relates to electrical apparatus,

such as current-limiting reactors of the oil-im mersed type, andparticularly to means for shielding the casing or tank surrounding thereactor coils from the stray or leakage magnetic flux that mightotherwise enter the wall of the easing structure.

If the casing for containing the reactor is of the usual steelconstruction, the hysteresis and eddy current and other stray losses inthe casing wall may become very large due to the passage of the leakagemagnetic fluxalong the wall of the casing, thus causing excessiveheating and objectionableenergy losses therein.

The above-mentioned difliculties may be overcome by providing a path oflow magnetic reluctance in the region between the casing and the reactorwinding for shunting the lines of magnetic flux away from the walls ofthe casing. Such magnetic shield structures have been used built in aspart of the winding-assembly and removable from the casing with thewinding. Such construction is, however, satisfactory only with thesmaller sizes of reactors and require extra heavy'coil supporting parts.Magnetic shield structures separate from the reactor winding assemblieshave also been used consisting of sheets of magnetic sheet materialexsection is graded. to the amount of flux to be carried by it so thatthe central portion lengthwise of the structure, which must carry thelargest amount of flux, may have a greater eflecshield unit structureswith the wall of the cas- .Htinuev along the tank wall,

tending between upper and lower supporting rings comprising a structureseparate from the winding assembly and separate from the tank or casingstructure, and which assembly is positioned and supported in the casingstructure sep- ,arately from the winding assembly. Such magnetic shieldstructures are diificult to handle and to properly brace within thecasing, and special precautions must be taken to provide insulatedjoints in the upper and. lower supporting rings and to insulate themfrom the casing in order. to avoid excessive losses.

In accordance with my invention, a plurality of individual bundles ofpunchings of ribbon-like strips of magnetic sheet steel plates isprovided, and the strips of each bundle tacked together, for example, byrunning beads of welds across the back of the bundle, that is, on theside thereof to be mounted nearest to the tank or casing wall. The endsof the ribbon-like strips are then welded to steel terminal plates,which are in turn welded to the inner wall of the casing structure so asto mount the bundles of strips of magnetic material in spaced relationto the casing wall.

Each bundle of strips of magnetic material, together with the terminalplates at each end thereof, comprises a separate unit which is easy tohandle, and after being welded to the tank wall becomes a part of thetank structure. By interleaving different lengths of punchings, it is,possible to construct the shields so that the crossing, flux whichenters the casing wall above and below the shield can enter and passalong the shield structure, instead of being forced to conthus resultingin lower losses.

One object of the invention is the provision of a magnetic shield forshielding the casing enclosing an oil-immersed reactor from the eflectsof leakage flu'x that is simple andeconomical to manufacture, eflicientin operation, easy to handle, and that is strongly braced againstshipping and short-circuiting forces.

Other objects and advantages of my invention will be apparent from thefollowing description of a preferred embodiment, reference being had tothe accompanying drawing in which:

Figure 1 is a top view of a casing structure, with the cover removed,showing the outline of a three-phase reactor positioned therein andshowing the location of the bundles of steel plates arranged inaccordance with the invention;

Fig. 2 is a vertical sectional view of a portion of the casing showingthe location of a bundie of sheet steel strips comprising a shield unitstructure and the location of the reactor wind= ing, and indicating indotted lines the general path of the lines of leakage magnetic flux;

Fig. 3 is a front elevational view of one of the individual unitstructures comprising the shield; and

Fig. 4 is a rear elevational view of the same structure prior to itsattachment to the casing wall.

p In the drawing, a casing structure I, having an upper outwardlyextending flange 2 for supporting the cover, is shown containingwindings 3 of a three-phase reactor structure. A plurality of shieldingunits 4 are shown separately attached to the inner wall of the casingand extending to an. elevation above the top and below the bottom of thewinding 3 in the region between the winding and the casing wall in whichthe leakage magnetic flux is'large. Re-

ierring particularly to Figs. 3 and 4, the bundle 5 oi strips ofmagnetic sheet material may comprise certainstrips that extend from thetop 6 of the bundle to an elevation 1 near the lower end of the bundleof strips, and certain of the strips may extend from the bottom 8 of thebundle upwardly to an elevation 9. Between the top 6 of the bundle andthe elevation 9, and also between the bottom 8 and the elevation I, thenumber of strips will, therefore, be half of those between elevations Iand 9 comprising the central portion of the unit. If desired, additionalstrips of magnetic material of shorter length may also be fitted betweenthose shown to additionally widen the unit for a desired portion of itslength.

A steel terminal plate H is provided adjacent the top of the bundle ofstrips and is welded thereto by running beads of weld l8 and I2, asshown in Fig. 3, and a similar lower terminal plate I3 is provided atthe lower end of the bundle which is welded to the strips at l9 and H.Running .beads of weld may also be applied across the edges of thebundle of strips at spaced intervals, as shown at l5 in Figs. 4 and2.Preferably, these beads of weld are positioned on the back of thebundle; that is, the side adjacent to the casing wall. The shield ismade up of 'a plurality of the structural units oi the character shownin Figs. 3 and 4 positioned about the inner wall of the casing, as shownin Fig. 1, and attached thereto by welds on the upper and lower edges ofthe terminal plates II and I3, as shown at I6 and H in Fig. 2. This typeof shielding structure is very economical of shielding material, sinceit is possible to space the indi idual units in accordance with theamount of shielding neededyso that on parts of the casing wall wheregreater Shielding is needed these units may be spaced closely togetheralong the casing wall, whileon parts of the wall where less shielding isneeded they may be spaced further apart and still provide adequateshielding. Also, the amount of material in difierent struc tural unitsmay be varied by using strips 5 having difierent widths, so that alarger cross-section of material may be provided by using wider ribbonstrips where more shielding is desired. The number of strips used in aparticular unit may also be varied, if desired, so that this type ofconstruction is not only economical oi the space required for it withinthe casing structure, but also makes the more efficient use of shieldingmaterial readily controllable.

It will be apparent to those skilled in the art that modifications oithe structural details may be made Within the spirit of the invention,and I do not wish to be limited otherwise than by the scope of theappended claims.

I claim as my invention:

1. In a current-limiting reactor, a reactor winding, a casing ofmagnetic material about the winding, a magnetic shield between thewinding and the casing comprising a plurality of units separatelyattached to the casing and each comprising a plurality of strips ofmagnetic material attached together to form a compact bundle, andterminal plates attached to the sides of said bundle of strips and tothe side wall of the casing for supporting the bundles in spacedrelation from thecasing wall, at least certain of said strips having alength less than the length of th bundle and so arranged in the bundlethat the number of strips in the end portions of the bundle. is lessthan the number comprising the central portion thereof.

2. In a current-limiting reactor, a reacton winding, a casing ofmagnetic material about the winding, a magnetic shield between thewinding and the casing comprising a plurality of units separatelyattached to the casing and each comprising a plurality of strips ofmagnetic material attached together to form a compact bundle andterminal plates welded to the sides of said bundle of strips adjacenttheir ends, said terminal plates being welded to said casing wall tosupport the bundles of strips in spaced relation from the casing walland from each other.

3. in a current-limiting reactor, a casing of magnetic material, areactor assembly therein including an electrical winding having its axispositioned vertically within the casing, a magnetic shield between thewinding and the casing comprising a plurality of units each comprising,a plurality of strips of magnetic material attached together atintervals by beads of welds across the back of the strips, said unitsbeing positioned vertically within the casing and attached to the innerside wall of the casing inspaced relation therefrom, said-strips havinga length less than the length of the bundle and so arranged in thebundle that certain strips extend from one end of'the bundle to alocation spaced from the other end and the remaining strips extend fromthe other end to a location remote from the first providing overlap ofthe strips in the central portion of the bundle.

4. In a current-limiting reactor, a casing of magnetic material, areactor assembly therein including an electrical winding having its axispositioned vertically within the casing, a magnetic shield between thewinding and the casing comprising a plurality of units each comprising aplurality of strips of magnetic material attached together at intervalsby beads of welds across the back of the strips, said units beingpositioned vertically within the casing, and terminal plates of magneticmaterial attached to the ends of said units and to the inner side Wallof the casing to support the strips of magnetic material in spacedrelation from the casing wall to provide a continuous magnetic paththrough the strips from the upper side wall to the lower side Wall.

5. In a current-limiting reactor, a casing of magnetic material, areactor assembly therein including an electrical winding having its axispositioned vertically within the casing, a magnetic shield between theWinding and the casing comprising a plurality of units each comprising aplurality of strips of magnetic material attached together at intervalsby beads of Welds across the back of the strips, said units being pdsitioned vertically within the casing, and terminal plates of magneticmaterial attached to the ends of said units and to the inner side wallof the casing to support the strips of magnetic material in spacedrelation from the casing wall to provide a continuous magnetic paththrough the strips from the upper side wall to the lower side wall, atleast some of said strips of magnetic material having a length less thanthat of the group of strips so that a lesser than the whole number ofsaid strips are attached to the terminal plates, thus providing agreater crosssection of active magnetic material in the central portionof the unit than adjacentthe ends.

LOUIS E. SAUER.

